Current

General

Functional Description

Current shows the filtered effective value of the actual current in milliampere (mA). The current is smoothed using a first order filter and a filter constant of one millisecond (t = 1 ms). The parameter Direction must be taken into account when interpreting Current.

For three-phase current motors, the total current consists of two parts:

oThe magnetizing current Id

oThe torque-forming current Iq

The overall current is calculated as follows:

I = sqrt (Iq² + Id²)

The Current parameter only displays the torque-forming current. The magnetizing current of synchronous motors is usually equal zero. In this case, the following applies (simplified):

I = Iq

The magnetizing current of asynchronous motors is constant and is calculated as follows:

Id = NomCurrent * sqrt (1 - cos phi)

For this, the torque-forming current cannot reach the peak current of the drive but only the possible value:

Max_Iq = sqrt (MaxDrivePeakCurrent² - Id²)

The value of Current is calculated once per Sercos cycle (CycleTime).

Since a delay occurs through the 1. filter order in addition to ShaftDelay, the following is defined:

CurrentDelay = ShaftDelay + 1 ms

Relative to the current effective value of the actual motor current, the Current is delayed by the time CurrentDelay. This means, a current is displayed that is delayed to the motor current by the time CurrentDelay.

NOTE: The parameter value is transferred from the slave to the master via the real-time channel of the Sercos. If the Sercos bus is not in phase 4, then a standard value is indicated here. If the Sercos bus is in phase 4 (operating phase), then the parameter value is transferred and indicated via the Sercos bus.